1. Field of the Invention
The present invention relates to a method of manufacturing tyres, and to the manufacturing apparatus to put the method into practice.
2. Description of the Related Art
A tyre generally comprises a carcass structure including at least one carcass ply having end flaps in engagement with respective annular anchoring structures, each of which is usually formed of a substantially circumferential annular insert to which at least one filling insert is applied at a radially outer position.
Associated with the carcass structure is a belt structure comprising one or more belt layers, disposed in radial superposed relationship with respect to each other and to the carcass ply, and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. Applied to the belt structure, at a radially external position, is a tread band made of elastomer material like other semifinished products constituting the tyre.
It is to be herein pointed out, to the aims of the present description, that by the term “elastomer material” it is intended a composition comprising at least one elastomer polymer and at least one reinforcing filler. Preferably, this composition further comprises additives such as a cross-linking agent and/or a plasticizer, for example. Due to the presence of a cross-linking agent, this material can be cross-linked through heating so as to form the final article of manufacture. Respective sidewalls of elastomer material are further applied to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads.
The carcass structure and belt structure together with the respective tread band, may be also provided to be made separately of each other in respective work stations, to be mutually assembled at a later time.
In accordance with conventional building methods the tread band and sidewalls are each made of a continuously extruded section member that, after being cooled to stabilise its geometrical conformation, is stored on suitable tables or reels. The semifinished product in the form of sections or made up of a continuous strip is then sent to a feeding unit the function of which is to pick up the sections or to cut sections of predetermined length from the continuous strip, each of these sections constituting the tread band or one of the sidewalls to be circumferentially applied to the tyre being processed.
In accordance with documents WO 00/35666 and WO 01/36185, in the name of the same Applicant, some tyre components, among which the tread band and sidewalls for example, are obtained through supply of an elongated element from an extruder, to be suitably distributed on the drum carrying the tyre being processed, while the latter is rotated around its own axis. Simultaneously, the support drum hanging from a robotized arm, is moved in front of the extruder to cause a transverse distribution of the elongated element and therefore form a plurality of circumferential coils with the latter, the coils being disposed in axial side by side and/or radial superposition relationship to define the structural tyre component.
In document WO 04/041522, in the name of the same Applicant as well, the carcass structure is provided to be formed through assembling of semifinished products on a support drum, to be subsequently coupled with the belt structure made on an auxiliary drum. The support drum used during the step of coupling the carcass structure with the belt structure is picked up by a robotized arm that will sequentially transfer and conveniently handle it in front of a series of extruders each set to lay on the carcass and/or the belt structure, a respective continuous elongated element of elastomer material having physico-chemical features specifically selected depending on the type of component that the individual extruder is designed to produce. More particularly, a first extruder is set to supply a first continuous elongated element directly against the belt structure, to form the tread band.
When manufacture of the tread band calls for formation of a so-called underlayer, an auxiliary extruder is provided to directly lay an auxiliary elongated element against the belt structure, before intervention of the first extruder, which auxiliary element is designed to form said underlayer of a suitable elastomer material.
A further extruder will supply a third continuous elongated element directly against the carcass ply, simultaneously with winding of the elongated element itself on the carcass structure carried by the drum, to make the tyre sidewalls.